The standard reduction potentials are given as: $E^\circ_{\text{Sn}^{4+}/\text{Sn}^{2+}} = +0.15 \text{ V}$ $E^\circ_{\text{Cr}^{3+}/\text{Cr}} = -0.74 \text{ V}$

The species with the higher (more positive) standard reduction potential will act as the cathode (undergo reduction), and the one with the lower (more negative) standard reduction potential will act as the anode (undergo oxidation). Thus, the $\text{Sn}^{4+}/\text{Sn}^{2+}$ couple acts as the cathode and the $\text{Cr}^{3+}/\text{Cr}$ couple acts as the anode.

The standard cell potential ($E^\circ_{\text{cell}}$) is calculated using the formula: $E^\circ_{\text{cell}} = E^\circ_{\text{cathode}} - E^\circ_{\text{anode}}$ $E^\circ_{\text{cell}} = +0.15 \text{ V} - (-0.74 \text{ V})$ $E^\circ_{\text{cell}} = +0.15 \text{ V} + 0.74 \text{ V} = +0.89 \text{ V}$